The present invention relates to a method for fabricating a memory device, and more particularly, to a method for fabricating a resistive memory device using the resistance variation depending on a supplied voltage such as a non-volatile resistive random access memory (ReRAM).
Recently, studies on next generation memory devices substitutable for a dynamic random access memory (DRAM) and a flash memory are actively being performed.
One of the next generation memory devices is a resistive memory device including a variable resistance material that has the resistance sharply changed according to a voltage supplied thereto and thus switches between at least two different resistance states. The resistive memory device stores different data, e.g., bit data ‘0’ or ‘1’, using the resistance variation of the variable resistance material.
FIG. 1A illustrates a view showing a structure of a conventional resistive memory device, and FIG. 1B illustrates a graph representing a current/voltage characteristic of the resistive memory device described in FIG. 1A.
As illustrated in FIG. 1A, the conventional resistive memory device includes one transistor A used as a switching element and one resistance element B used as a storing element. Herein, the resistance element B includes a lower electrode 11, an upper electrode 13 and a variable resistance material 12 disposed between the lower electrode 11 and the upper electrode 13.
Each of the lower electrode 11 and the upper electrode 13 may include one selected from a group consisting of aluminum (Al), platinum (Pt), ruthenium (Ru), iridium (Ir), nickel (Ni), titanium nitride (TiN), titanium (Ti), cobalt (Co), chromium (Cr), tungsten (W), copper (Cu) and an alloy thereof.
The variable resistance material 12 includes a binary oxide such as a transition metal oxide, e.g., NiO, TiO2, HfO, Nb2O5, ZnO, ZrO2, WO3 or CoO, or a perovskite series material, e.g., STO (SrTiO), PCMO (PrCaMnO) or GST (GeSbTe). Moreover, a metal oxynitride such as TiON was recently turned out to have a characteristic of the variable resistance material.
According to a voltage supplied between the lower electrode 11 and the upper electrode 13, the conventional resistive memory device shows the current/voltage characteristic described in FIG. 1B.
As shown in FIG. 1B, if the supplied voltage is lower than A1 or greater than A2, the resistive memory device shows a current/voltage characteristic following a B1 curve. Meanwhile, if the supplied voltage is between A1 and A2, the resistive memory device shows a current/voltage characteristic following a B2 curve.
Therefore, if a certain read voltage A3 lower than A1 is supplied to the resistance element B after a voltage between A1 and A2 is supplied, there is measured a current following the B2 curve. On the other hand, if the certain read voltage A3 lower than A1 is supplied to the resistance element B after a voltage greater than A2 is supplied, there is measured a current following the B1 curve.
After all, a value of a current outputted in a reading operation is changed according to a voltage supplied between the upper electrode and the lower electrode. That is, the resistive memory device shows different resistance states according to the variation of the voltage supplied between the upper electrode and the lower electrode.
FIGS. 2A to 2C illustrate cross-sectional views of a method for fabricating a conventional resistive memory device.
Referring to FIG. 2A, a lower electrode 21 is formed over a substrate (not shown) where a certain underlying structure is formed.
Then, as illustrated in FIG. 2B, a variable resistance material layer 22 is formed on the lower electrode 21.
Herein, before forming the variable resistance material layer 22, a cleaning process may be additionally performed to remove foreign substance existing on an interface of the lower electrode 21 and the variable resistance material layer 22.
Referring to FIG. 2C, an upper electrode 23 is formed on the variable resistance material layer 22.
However, the method for fabricating the conventional resistive memory device has the following problems.
First of all, an interface characteristic of the lower electrode and the upper electrode is important in securing the characteristic as the resistive memory device. In particular, no foreign substance should be on the interface of the lower electrode and the variable resistance material layer. For this purpose, a separate cleaning process should be performed between a process of depositing the lower electrode and a process of depositing the variable resistance material layer.
Further, at least three deposition processes are required to fabricate the resistive memory device, wherein the deposition processes include the process of depositing the lower electrode, the process of depositing the variable resistance material layer and a process of depositing the upper electrode.
Therefore, a technology for improving a characteristic of a device as well as employing a simpler fabricating process than the method for fabricating the conventional resistive memory device may be useful.